Cyclic ethers to esters and monoesters to bis-esters with unconventional coupling partners under metal free conditions via sp³C–H functionalisation

Abstract

An efficient metal free oxidative esterification of sp(3) C-H bonds (adjacent to an oxygen atom) in simple solvents like 1,4-dioxane, tetrahydropyran, tetrahydrofuran and ethyl acetate has been achieved using terminal aryl alkenes and alkynes as the ArCOO(-) sources.

Organocatalysis in Inert C–H Bond Functionalization

“…In 2011, Wan and co-workers described the catalytic formation of α-acyloxy ethers involving CDC reaction of ether and carboxylic acid (Scheme ). The combination of catalytic amounts of TBAI with excess TBHP as oxidant was efficient for generating tert -butoxyl radical t -BuO • , which participates directly for abstracting α-H to an α-oxyl radical. An oxocarbenium intermediate generated from further oxidation of the radical was proposed as the active intermediate, which was then intercepted by a number of nucleophiles including carboxylic acid, amide, and tetrazoles (Scheme ).…”

nBu4NI‐Catalyzed α‐Benzoxylation of Ketones with Terminal Aryl Alkenes

“…Similarly, when 1‐naphthyl tert ‐butyl perester was treated with ketone 2a , the desired α‐benzoxylation product 3ka was isolated in 57 % yield. Thus, it can be envisaged that styrene under the influence of TBAI/TBHP is transformed into either benzoic acid or a tert ‐butyl perester through phenyl glyoxal and benzaldehyde intermediates (Scheme ) 3f. Meanwhile, in the presence of a formed tert ‐butoxy radical, α‐carbonyl radical 4 is generated 15.…”

“…With regard to functional group transformations, employing a surrogate is useful and often necessary. Recently, Patel and co‐workers demonstrated the use of aryl alkenes as an arylcarboxy surrogate under metal and metal‐free conditions 3f,14. Herein, we have used aryl alkenes as an arylcarboxy surrogate for the α‐benzoxylation of ketones and obtained good yields for a variety of ketones under metal‐free conditions.…”

Pd(ii)-catalysed o-aroylation of directing arenes using terminal aryl alkenes and alkynes

“…A possible pathway for the formation of phenylglyoxal (C), benzaldehyde (D), benzoic acid (E) (except (B)) from styrene has been recently demonstrated by us. 6,21 To deduce the nature of the reaction a standard reaction was carried out in the presence of a radical quencher, TEMPO. Detection of TEMPO-ester (Y) along with substantial drop in product yield (9%) of (7a) suggests the radical nature of the reaction (Scheme 3, experiment VI).…”